Realistically, you won't have a case in court.

Despite emotional attachment to a vehicle, the vehicle is only worth in real life what it is bluebooked at. A 93 Z28 is going to be worth $3000-3500 at the MOST, especially when you can get a 98-2000 LS1 Z28 with 100,000+ miles on it the same miles on it for $4000-5500.

If you felt that the vehicle is worth more than bluebook, then you should have asked your insurance company to add additional insurance to it for mods, etc...Which is why in most cases the insurance company asks you to make them aware of any modifications done to the vehicle... Sort of like homeowners insurance -- when you upgrade your house, the value goes up and it would be intelligent to add more protection to your policy.

Lesson learned.